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Abstract:

A directional coupler is disclosed integrated on a single chip and an
integrated circuit based on a standard CMOS process and relates to a
field of radio frequency communication. In exemplary implementations, by
using a standard CMOS process technology, the directional coupler
integrated by a CMOS process is formed by a coil winded by a upper layer
of metal lines, a coil winded by a lower layer of metal lines, two tuning
capacitor array, and a matching resistor. Two terminals of the coil are a
direct terminal and an input terminal; two terminals of the coil are a
coupled terminal and an isolation terminal; the terminals of the coils
and are intersected at 90°; the coil is winded by an upper metal
layer and the coil is winded by a lower metal layer. Further, the
insertion loss is low and the isolation degree is large.

Claims:

1. A directional coupler based on a CMOS process, comprising the
following steps: (1) a coil 1 which is winded by a Mth metal layer and is
connected between an input terminal (Input) and a direct terminal
(Direct), and an intersect portion of which is connected by (M-1) th
metal layer; a coil 2 which is winded by an Nth metal layer and is
connected between a coupled terminal (Coupled) and an isolated terminal
(Isolated), and an intersect portion of which is connected by (N+1) th
metal layer and the coil 1 and the coil 2 form a stereochemical
structure, wherein N≧1,M≧N+2; (2) the coils 1 and 2 are
winded in a shape of a square, a circle, a rectangle, an octagon or other
polygon; (3) two ends of the coil 1 and two ends of the coil 2 form an
angle of 90.degree., a distance between the direct terminal (Direct) and
the coupled terminal (Coupled) is small while a distance between the
input terminal (Input) and the coupled terminal (Isolated) is large; (4)
metal lines of the coil 1 and the coil 2 are intersectly arranged
vertically, centers of upper/lower layer metal lines are alignned with
centers of lower/upper layer metal lines, the upper and lower layer metal
lines have an excessive overlap (O), that is, a line width of the metal
line is larger than or equal to or smaller than an interval S between the
metal lines; (5) an adjustable capacitor array Cp is disposed between the
input terminal and the direct terminal to achieve a frequency tuning; and
(6) an adjustable capacitor array Cs is disposed between the coupled
terminal and the isolated terminal to achieve an isolation degree tuning.

2. An integrated circuit used for a directional coupler tuning
technology, wherein, the integrated circuit comprises an integrated
directional coupler according to claim 1, and the directional coupler
changes a frequency of a lower concave point of an isolation degree curve
by changing the adjustable capacitor array Cp, and changes a down
concaved depth of the isolation degree curve by changing the adjustable
capacitor array Cs.

3. The integrated circuit of claim 2, wherein, the integrated circuit is
fabricated by a standard CMOS process or a BiCMOS/BJT/HBT process.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority to a Chinese application
No. 201110399962.5, filed on Dec. 5, 2011, which is incorporated herein
by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to the field of a radio frequency
integrated circuit technology, and particularly relates to a on-chip
integration directional coupler and an integrated circuit by using a
standard CMOS process.

BACKGROUND OF THE INVENTION

[0003] A directional coupler is a radio frequency device widely used for a
signal isolation, a signal separation, etc., and is used to make a radio
frequency receiver and a radio frequency transmitter operate at the same
frequency band. FIG. 1 illustrates a principle of a directional coupler
used in a transceiver system, an input terminal (Input) is connected to
an output terminal of a transmitter (TX), and a direct terminal (Direct)
is connected to an antenna (Antenna), a coupled terminal (Coupled) is
connected to an input terminal of a receiver (RX), an isolated terminal
(Isolated) is connected to a matching resistor (Res). There are some
definitions for the directional coupler. A loss from the input terminal
to the direct terminal is referred as an insertion loss (Insertion Loss),
a loss from the input terminal to the coupled terminal is referred as a
coupling degree (Coupling), a loss from the direct terminal to the
coupled terminal is referred as an isolation degree (Isolation), a
difference between the isolation degree to the coupling degree is
referred as directivity (Directivity). It is required that the insert
loss is very low, the coupling degree is not very large, and the
isolation degree is very large, that is, the directivity is strong. For a
transceiver system with the same frequency for receiving and
transmitting, the energy for transmitting a signal is generally large and
a large portion thereof may be coupled to the input terminal of the
receiver, however, a receiving signal is very weak and a very strong
output coupling signal may affect the useful receiving signal if a
directional coupler is not used, which may cause the receiver not operate
properly, as shown the left part of FIG. 2. After the directional coupler
is used, the receiving signal may be partially lost due to the coupling
degree, and meanwhile the transmitting signal coupled to the input
terminal is greatly attenuated. Thus, the transceiver with the same
frequency for receiving and transmitting may operate properly, as shown
the right part of FIG. 2.

[0004] Generally, a conventional directional coupler is fabricated by
using a transmission line, as described in a reference (Hilal Ezzeddine
et al., "Directional coupler", U.S. patent, U.S. Pat. No. 7,394,333 B2,
Jul. 1, 2008). The conventional directional couplers have a large volume,
complicated assembling processes and high costs. Then, in order to
miniaturize the directional coupler, separated components are used, as
described in a reference (Oleksandr Gorbachov, "Directional coupler for
RF power detection", U.S. patent, U.S. Pat. No. 7,576,626 B2, Aug. 18,
2009). However, such a directional coupler is still unable to be
integrated. With the rapid development of the integrated circuit, the
on-chip integration is a tendency in future. An integrated directional
coupler expands the applicability and has a lower cost, and is applied
for, for example, a radio frequency identification (RFID Reader) and so
on. In order to implement a on-chip integration for the directional
coupler, some special processes are employed, as shown in a reference
(Shim, S., Hong, S., "A CMOS Power Amplifier With
Integrated-Passive-Device Spiral-Shaped Directional Coupler for Mobile
UHF RFID Reader," Microwave Theory and Techniques, IEEE Transactions on ,
vol. PP, no. 99, pp. 1, 0). The reference describes a directional coupler
fabricated by using an integrated passive device (IPD) process. Though
the directional coupler has a small volume, a special processing
technology that can not be compatible with a standard CMOS process is
used, the cost is high, and a complicated process is used. Thus, it is
difficult to achieve an over-chip integration for the directional
coupler, and the practical applicability of the directional coupler is
limited.

[0005] At present, the solution or technology for implementing the
directional coupler as described in the known references and patents do
not implement the directional coupler by using a standard CMOS process,
which greatly limits the application range thereof. For example, in the
field of the mobile communication system, miniaturization and portability
are highly required. Though some directional couplers have met the
requirement of miniaturization, the usage of special process causes a
high cost and it is hardly to meet the requirements of the system
integration.

SUMMARY OF THE INVENTION

[0006] Therefore, it is an object of the present invention to provide a
directional coupler integration technology and an integrated circuit
based on a standard CMOS process. The technology has a feature that the
on-chip integration can be achieved by using a standard silicon-based
CMOS process, and has a small area, a low input loss, a high coupling
degree, a high isolation degree and a strong tuning ability.

[0007] The above object of the present invention is achieved by the
following technical solution.

[0008] A directional coupler integration technology and integrated circuit
based on a standard CMOS process are provided as follows (as shown in
FIGS. 3 and 4).

[0009] (1) A coil 1 is provided between an input terminal (Input) and a
direct terminal (Direct) and is winded by a Mth metal layer, and an
intersect portion thereof is connected by (M-1) th metal layer; a coil 2
is provided between an input terminal (Input) and an isolated terminal
(Isolated) and is winded by an Nth metal layer, and an intersect portion
thereof is connected by (N+1) th metal layer, wherein N≧1,
M≧N+2. Thus, a stereochemical structure is formed.

[0010] (2) The coils 1 and 2 are winded in a shape of a square shape, a
circle shape, a rectangle shape, an octagon shape or other polygon shape.

[0011] (3) The two ends of the coil 1 and the two ends of the coil 2 form
an angle of 90°, the distance between the direct terminal (Direct)
and the coupled terminal (Coupled) is small, while the distance between
the input terminal (Input) and the coupled terminal (Isolated) is large.

[0012] (4) Metal coils of the coil 1 and the coil 2 are intersectly
arranged, a center of an upper/lower metal line is alignned with a center
of a lower/upper metal line, the upper and lower metal lines have an
excessive overlap O (also may have no excessive overlap), that is, the
line width W of the metal line may be larger than or equal to or smaller
than the interval S between the metal lines.

[0013] (5) An adjustable capacitor array Cp is disposed between the input
terminal and the direct terminal to achieve a frequency tuning.

[0014] (6) An adjustable capacitor array Cs is disposed between the
coupled terminal and the isolated terminal to achieve an isolation degree
tuning.

[0015] The principle of the present invention is described as follow.

[0016] (a) A directional coupler is equivalent to a passive transformer
with a changed structure. For a general passive transformer, four
terminal parameters are symmetrical. However, the directional coupler
uses the asymmetry of space and position to effect the differences among
the four terminal parameters. Two terminals of coil 1 (in this
disclosure, the coil 1 may be square, rectangle, circle, octagon or other
polygon) winded by a Mth metal layer and two terminals of coil 2 (in this
disclosure, the coil 1 may be square, rectangle, circle, octagon or other
polygon) winded by a Nth metal layer are perpendicular at 90°. By
using the space asymmetry, the four terminal circuit parameters are
different and show a directionality. The direct terminal (Direct) and the
input terminal (Input) are two terminals of an identical layer of coil.
The coupled terminal (Coupled) and the isolated terminal (Isolated) are
two terminals of another identical layer of coil. The distance between
the direct terminal (Direct) and the coupled terminal (Coupled) is small
and the distance between the input terminal (input) and the isolation
terminal (Isolated) is larger.

[0017] (b) The coils 1 and 2 have different shapes, radiuses (minimum
inner radius is D1 and maximum outer radius is D2) and coil numbers. The
coils 1 and 2 may use metal lines with different line widths W and
different intervals S. The insertion loss (Insertion Loss), coupling
degree (Coupling), isolation degree (Isolation) and directivity
(Directivity), etc. may be adjusted by changing the metal line at
different layers (or by changing the vertical interval between the upper
metal line and the lower metal line).

[0018] (c) Generally, the directional coupler is designed so that the
outputs of power amplifiers are well matched. However, in practice, the
outputs of the transmitter power amplifier are poorly matched and
variations of output power may lead to variation of the match of the
power amplifier, so that there is a deviation between the practical
performance and the design value of the directional coupler. In
additional to the above problems, the factors such as process fluctuation
and temperature variation and the like may cause deterioration of
performance of the directional coupler.

[0019] The directional coupler uses a capacitor Cp for a frequency tuning
and a capacitor Cs for an isolation degree tuning to address the above
problems.

[0020] The present invention has the following advantages.

[0021] (1) The input loss is low. The input terminal (Input) and the
direct terminal (Direct) are connected by a Mth metal layer (at the
crossing connected by (M-1)th metal layer), an upper metal layer (with
respect to a metal layer used by another layer of coil) has a small
parasitic capacitance with respect to the ground, and the matching
resistor of an isolation terminal of a lower layer of coil are grounded,
a portion of a parasitic capacitance of the upper layer of coil is
shielded by the lower layer of coil, so that the input loss is very
small.

[0022] (2) The directivity is good. The present invention uses a
stereochemical coil structure which includes a coil 1 formed by a Mth
metal layer and a coil 2 formed by an Nth metal layer (N≧1,
M≧N+2), and a vertical distance H is larger. The upper and lower
metal layer are intersectly arranged in a vertical direction, line width
centers of upper/lower metal layer and interval centers of lower/upper
metal lines are aligned with each other in the vertical direction. There
is an excessive overlap (also no the excessive overlap) at the edge of
the metal layer. Those features mentioned above make the isolation degree
greatly increase, the directivity become better, as shown in FIG. 5 (a
simulation result at the operation frequency of the transceiver is 875
MHz).

[0023] (3) The area is small. Since the stereochemical coil structure is
used and the upper and lower metal layer are intersectly arranged, in the
case of the same identical directivity requirement, the interval between
the metal lines may be smaller, the whole structure of the directional
coupler may be more compact and area thereof may be smaller, as compared
with a flat coil structure.

[0024] (4) The applicability range is wide. During the design process, by
changing the shapes (e.g. square, rectangle, circle, polygons such as
octagon), coil numbers, radiuses (minimum inner radius D1, maximum outer
radius D2) of the coils 1 and 2, the interval between the metal layers
used by coils 1 and 2 (e.g. selecting the metal at different layers as
the lower or upper layer to change the vertical interval H between the
upper and lower layer of metal coil), and the depth O excessively
overlapped between two coils, the magnitudes of insertion loss, coupling
degree, isolation degree and directivity may be flexibly changed. Also,
the above factors may be changed to meet with different requirements of
different systems.

[0025] (5) The tuning ability is good. A capacitor Cp is introduced for a
frequency tuning and a capacitor Cs is introduced for an isolation degree
tuning. As such, the actual operation of the device may be prevented from
deteriorating due to the nonideal effects resulted from a poor matching
between the outputs of the transmitters (TX), and a varied output
matching under different output powers, a process fluctuation and a
temperature variation.

[0026] (6) The device of the present invention may be integrated into a
single chip with the standard silicon-based CMOS process and may also be
integrated with a BiCMOS process, a HBT process and so on. The device may
be used as a module to be integrated with other circuits and systems over
a single chip. Thus, a cost is reduced, and system integration degree may
be greatly increased.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be described in more detail below in
conjunction with the attached drawings.

[0028] FIG. 1 is a principle diagram of a directional coupler used in a
general transceiver system;

[0029] FIG. 2 is a principle diagram of a directional coupler for
restraining the coupling portion of a transmitting signal in a receiving
signal;

[0030] FIG. 3 is plan view showing a layout of a novel directional coupler
based on a standard CMOS process of the present invention;

[0031] FIG. 4 is cross sectional view taken along a line A3 of the layout
of the novel directional coupler based on a standard CMOS process of the
present invention;

[0032] FIG. 5 is a graph showing the performance of the novel directional
coupler based on a standard CMOS process of the present invention; and

[0033] FIG. 6 is a schematic diagram of an embodiment of the present
invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] For the purpose of detailed illustration of the present invention,
a specified embodiment is described below.

[0035] A directional coupler integrated by a CMOS process of the present
invention may be connected to a transmitter, a receiver, an antenna and a
matching resistor to form a transceiver which operates at the same
frequency simultaneously. As a radio frequency identification reader
achieved by the present invention shown in FIG. 6, the receiver and the
transmitter may be simultaneously operated at the same frequency.

[0036] A terminal 1 in FIG. 6 is an input terminal (Input) of the
directional coupler integrated by CMOS process, a terminal 2 in FIG. 6 is
a direct terminal (Direct), a terminal 3 in FIG. 6 is an isolated
terminal (Isolated), and a terminal 4 in FIG. 6 is a coupled terminal
(Coupled).

[0037] The directional coupler integrated by CMOS process may be connected
as shown in FIG. 6(a). The terminal 1 is connected with an output
terminal of the transmitter (TX), the terminal 2 is connected to the
antenna (Antenna), the terminal 3 is connected to a grounded resistor
(Res) of 50 ohm, and the terminal 4 is connected to an input terminal of
the receiver (RX). The definitions of respective parameters are as
follows: S12 (S21) corresponds to the insertion loss, S24 (S42)
corresponds to the coupling degree, and S14 (S41) corresponds to the
isolation degree.

[0038] The directional coupler integrated by CMOS process may also be
connected as shown in FIG. 6(b). The terminal 2 is connected with the
output terminal of the transmitter (TX), the terminal 1 is connected to
the antenna (Antenna), the terminal 4 is connected to the grounded
resistor (Res) of 50 ohm, and the terminal 3 is connected to the input
terminal of the receiver (RX). The definitions of respective parameters
are as follows. S12 (S21) corresponds to the insertion loss, S13 (S31)
corresponds to the coupling degree, and S23 (S32) corresponds to the
isolation degree.

[0039] The directional coupler integrated by CMOS process may also be
connected as shown in FIG. 6(c). The terminal 3 is connected with the
output terminal of the transmitter (TX), the terminal 4 is connected to
the antenna (Antenna), the terminal 1 is connected to the grounded
resistor (Res) of 50 ohm, and the terminal 2 is connected to the input
terminal of the receiver (RX). The definitions of respective parameters
are as follows. S34 (S43) corresponds to the insertion loss, S24 (S42)
corresponds to the coupling degree, and S23 (S32) corresponds to the
isolation degree.

[0040] The directional coupler integrated by CMOS process may also be
connected as shown in FIG. 6(d). The terminal 4 is connected with the
output terminal of the transmitter (TX), the terminal 3 is connected to
the antenna (Antenna), the terminal 2 is connected to the grounded
resistor (Res) of 50 ohm, and the terminal 1 is connected to the input
terminal of the receiver (RX). The definitions of respective parameters
are as follows. S34 (S43) corresponds to the insertion loss, S31 (S13)
corresponds to the coupling degree, and S14 (S41) corresponds to the
isolation degree.

[0041] A directional coupler technology and integrated circuit based on a
standard CMOS process is described through the specific embodiments
mentioned above, those skilled in the art of the filed may make various
change in terms of forms and contents according to the above steps
without departing from the substantial scope protected by the present
invention. Thus, the present invention is not limited to the content
disclosed in the embodiments.

Patent applications by Ru Huang, Beijing CN

Patent applications by Peking University

Patent applications in class For providing adjustable coupling

Patent applications in all subclasses For providing adjustable coupling